Method of making cuprous oxide



United States Patent 3,466,143 METHOD OF MAKING CUPROUS OXIDE Howard E. Day, Calumet, Mich., assignor, by mesne assignments, to Calumet & Hecla Corporation, Evanston,

Ill., a corporation of Delaware Filed Apr. 13, 1967, Ser. No. 630,750 Int. Cl. C01g 3/02 U.S. CI. 23-147 6 Claims ABSTRACT OF THE DISCLOSURE A method of producing cuprous oxide in which a mixture of copper oxides containing more than about 50% but less than all of the mixed oxides as cuprous oxide and about 03-12% ammonia is heated at about 800- 1300" F. in the presence of a preheated nonoxidizing inert gas flowing at a velocity of at least about seven feet per minute until at least a significant portion of the cupric oxide in the mixture has been reduced to cuprous oxide.

In the present invention the particulate mixture of cupric and cuprous oxides containing the above specified amount of cuprous oxide and ammonia is heated in a nonoxidizing inert gas atmosphere at a temperature of about 800-1300 F. until at least a significant portion of the cupric oxide of the mixed oxides has been reduced to cuprous oxide. In the preferred method the mixture of oxides is from an aqueous ammonical solution copper leaching process of the type disclosed in Benedict U.S. Patent 1,131,986.

The single figure of the accompanying drawing is a semischematic elevation of an apparatus for practicing the method of this invention in a continuous manner.

In the method of this invention the raw material comprises essentially a particulate mixture of cupric and cuprous oxides in which at least about 50% but less than all of the mixed oxides is cuprous oxide and the rest is cupric oxide. The preferred amount of cuprous oxide is about 75-85% of the total. The mixture also contains ammonia in an amount of about 0.31.2% and an ideal raw material mixture is the product of an aqueous ammoniacal solution copper leaching process which contains the ammonia as a residue thereof.

The mixture must be freshly prepared in that it must not be more than about four weeks old before subjecting the mixture to the method of this invention. Thus, where the mixture is the product of the above-mentioned copper leaching process, the particulate mixture must have been precipitated from solution not more than about four weeksbefore. Although the four weeks is a maximum, actually the shorter the time period before the mixture is subjected to the process of this invention the better. Furthermore, the lower the amount of cuprous oxide in the mixed copper oxides the shorter the time delay should be before the process is practiced. Thus, where the oxides are about 79% cuprous the time delay should not be more than about 10 days. However, where the mixture is about 84% cuprous the time delay can be up to about four weeks.

In practicing the method of this invention the mixture as described above is heated in the absence of oxygen at a temperature of about 8001300 F. with the lower temperature being used for high cuprous content feeding material while the higher temperature is used for feeds with relatively low cuprous content.

During the heating the copper oxide mixture is subjected to an inert non-oxidizing atmosphere such as one of nitrogen, carbon dioxide, mixed nitrogen and carbon dioxide and the like. During the heating of the mixture gaseous reaction products are given off and these include water, nitrogen, carbon dioxide and the like. The gas of the atmosphere is required to be inert in that it does not react with any of the components of the mixture or the products of the method of this invention.

In order that the process will be efficient the inert gas is preheated to 212 F. or above, and preferably about 250 F., in order that it may rapidly and efiiciently vaporize the water that is given oif as a byproduct. Any substantial amount of water present causes the particulate feed material mixture to cake and can block the apparatus used in practicing the invention.

The inert gas is preferably passed in contact with the heated feed material mixture at a linear velocity that is at least seven feet per minute and preferably not less than ten feet per minute. There is no maximum limit to this linear velocity although there is no practical reason to exceed about 20 feet per minute primarily because of cost.

In one method of practicing the invention the feed mixture is brought up to a temperature of the specified 800-1300 F. range as rapidly as possible so as to prevent substantial condensation of moisture on the material. If substantial amounts of moisture should condense, the feed material tends to cake as mentioned above and block the apparatus requiring frequent shutdowns in order to remove the cake.

The 0.3-1.2% ammonia in the feed material appears to provide a gentle reducing action which reduces the cupric oxide to cuprous without producing excessive amounts of metallic copper. At the temperature of the process ammonia appears to dissociate into nitrogen and hydrogen and apparently the hydrogen present provides the reducing action. This however is merely theory and the invention is not to be limited by this theory.

The single figure of the accompanying drawing illustrates one form of apparatus for practicing the invention. In this apparatus which is actually a rotary furnace or calciner there is provided a rotatable elongated cylinder 10 having attached thereto a supporting collar 1'1 adjacent each end each supported on rollers 29. The cylinder 10 is rotated by a variable speed drive 22 operating through sprockets 30 and 31 and a chain 32.

The cylinder 10 is insulated between the collars 11 by refractory insulation 12 and the central portion of the cylinder 10 is heated either by gas fired burners (not shown) or any other desired heating means to provide an entrance and heat zone 13 surrounded by the insulation 12.

In order to feed material into the cylinder 10 within the confines of the heat zone 13 there is provided a hopper 14 for the material from which extends the helical material conveyor 15 of the usual type within the customary feed tube 16.

The inner end of the conveyor 15 and feed tube 16 extends to within the adjacent end 17 of the heat zone 13 with the result that the material is introduced as indicated at 18 into the confines of the heat zone 13. The rotating cylinder 10 which has a slope from entrance end to exit end of any degree desired (such as one inch of slope to four feet of length to one inch of slope to eight feet of length) tumbles and directs the material through the heat zone 13 to the exit end where it is discharged as indicated at 19. At the discharge the material is either packaged immediately so as to prevent substantial oxidation or is protected by a nonoxidizing atmosphere in the customary manner. The cylinder 10 at about the middle of the heat zone 13 is provided with an upwardly projecting stack 20 for the gaseous combustion by-products.

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Columns 7-13 give the chemical composition of the feed material in the various examples with TRP in column 7 being the total reducing power as percent cuprous oxide, column 8 the percent of total copper in the feed material, column 9 the percent of metallic copper, column 10 the percent of cuprous oxide, column 11 the percent of cupric oxide, column 12 the total oxide content, and column 13 the percent of ammonia.

In column 14 the average particle diameter of the feed is given in microns while in column 15 is given the bulk density in pounds per cubic foot.

Columns 16-21 recite the chemical composition of the final product from the process of this invention. In column 16 the total reducing power is given while column 17 presents the total copper content, column 18 the metallic copper content, column 19 the cuprous oxide content, column 20 the cupric oxide content, and column 21 the total oxide content.

The percent cuprous oxide of column 19 is determined by subtracting 2.245 times the metallic copper percent of column 18 from the TRP percent of column 16. In many cases this number exceeds 100%. This is also true of the total oxide percent shown in column 21 and obtained by adding columns 19 and 20. The reason for this is not understood. The methods of analysis in all cases was taken from the Military Specification Pigment Grade Cuprous Oxide, MILP-15l619A (SHIPS), including amendment 1, June 9, 1960. This specification gives detailed directions for the analytical procedures and products are accepted or rejected on the basis of these analyses.

The final product is preferably at least about 86% total copper and is preferably at least 97% total reducing power expressed as cuprous oxide. When this reducing power is expressed as cuprous oxide it can be over 100%, as shown in the table. This is true because some of the reducing power is actually due to the metallic copper present which has a higher reducing power than cuprous oxide.

The amounts presented in the table are by weight.

Having described my invention as related to the embodiments set out heerin, it is my intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompany claims.

I claim:

1. The method of producing cuprous oxide, comprising: passing through a heating zone maintained at about 8001300 F. a freshly prepared particulate mixture containing about 0*.31.2% ammonia and mixed cupric and cuprous oxides of which more than about but less than all of said mixed oxides is cuprous oxide; and simultaneously passing a non-oxidizing inert gas preheated to a water vaporizing temperature of at least about 212 F. through said heating zone at a velocity of at least about seven feet per minute in intimate contact with the particles of said mixture, said mixture being maintained in said zone until at least a significant portion of said cupric oxide has been reduced to cuprous oxide, said amounts being by weight.

2. The method of claim 1 wherein said mixture is from an aqueous ammoniacal solution copper leaching process and contains said ammonia as a residue of said process, and said mixed oxides is about. -85% cuprous.

3. The method of claim 1 wherein said gas is preheated to above 212 F. prior to said passing through said heating zone and is passed countercurrently to said mixture.

4. The method of claim 1 wherein said mixture is initially contacted with said gas in said heating zone in order that said mixture will rapidly reach substantially said Zone temperature to prevent substantial moisture condensation from the gas on the mixture.

5. The method of claim 1 wherein said preheated gas is initially contacted with said mixture while the mixture is maintained in a loose condition.

6. The method of claim 5 wherein said loose condition is achieved by dropping said mixture vertically through a rising mass of said preheated gas.

References Cited UNITED STATES PATENTS 1,131,986 3/1915 Benedict 23-147 2,758,014 8/1956 Drapeau et a1. 23-l47 FOREIGN PATENTS 163,210 5/1921 Great Britain.

OSCAR R. VERTIZ, Primary Examiner HOKE S. MILLER, Assistant Examiner US. Cl. X.R. 23148, 279 

